Electron Microscopy Documents the Microorganisms’ Biodestructive Action on Polyurethane and the Production, Internalization and Vesicular Trafficking of Nanoparticles

Prostheses in the oral cavity are constantly attacked by microorganisms. Bacteria and fungi colonize these surfaces concurring in the material’s biodestruction; the corrosive action generates debris of different size, with particles ranging from few micrometers to nanometers. Transmission Electron Microscope (TEM), Scanning Transmission Electron Microscope (STEM) and Focused Ion Beam/Scanning Electron Microscope (FIB/SEM) used in this study show that bacteria (Staphylococcus aureus) and fungi (Candida albicans) are able to adhere to the prostheses’ surfaces (polyurethane) and operate a biodestructive process. Electron images document the damages on the polymeric surfaces and the formation of debris. Polyurethane nanoparticles can be detected not only outside the bacterial cells but even in cells, surrounded by membrane vesicles; this work ascertains that the uptake process occurs through endocytosis, and outlines that the cytoskeleton is implicated both in the nanoparticles internalization and in the vesicular trafficking within the bacterial cell. Polyurethane nanoparticles we studied are not engineered, have unexpected characteristics and reactivity; moreover being surrounded by vesicles within bacterial cells they raise a new problem in toxicology, since this represents a new way through which nanoparticles may gain access to the body (driven by bacteria-host cells interactions), elude the immune system reaction to xenobiotic elements and provoke pathologies.